International Ultraviolet Explorer
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| Names | Explorer 57 SMEX/IUE IUE |
|---|---|
| Operator | NASA / ESA / SERC |
| COSPAR ID | 1978-012A |
| SATCAT no. | 10637 |
| Website |
ESA Science and Technology NASA IUE Archive |
| Spacecraft properties | |
| Payload mass | 672 kg (1,482 lb) |
| Start of mission | |
| Launch date | 17:36:00, January 26, 1978 |
| Rocket | Delta 2914 |
| End of mission | |
| Disposal | Decommissioned |
| Deactivated | September 30, 1996 |
| Orbital parameters | |
| Reference system | geosynchronous orbit |
| Perigee | 26,000 km (16,000 mi) |
| Apogee | 42,000 km (26,000 mi) |
| Period | 24 hrs |
| Main | |
| Type | Ritchey-Chretien Cassegrain reflector |
| Diameter | 45 cm (18 in) |
| Focal length | f/15 |
| Wavelengths | Ultraviolet 115 nm to 320 nm |
| Instruments | |
| 115 nm to 198 nm Echelle spectrograph 180 nm to 320 nm Echelle spectrograph Lithium-drifted Silicon Particle Flux Monitor |
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 Legacy ESA insignia for the IUE mission |
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The International Ultraviolet Explorer (IUE) was an astronomical observatory satellite primarily designed to take ultraviolet spectra. The satellite was a collaborative project between NASA, the UK Science Research Council and the European Space Agency (ESA). The mission was first proposed in early 1964, by a group of scientists in the United Kingdom, and was launched on January 26, 1978 aboard a NASA Delta rocket. The mission lifetime was initially set for 3 years, but in the end it lasted almost 18 years, with the satellite being shut down in 1996. The switch-off occurred for financial reasons, while the telescope was still functioning at near original efficiency.
It was the first space observatory to be operated in real time by astronomers who visited the groundstations in the United States and Europe. Astronomers made over 104,000 observations using the IUE, of objects ranging from solar system bodies to distant quasars. Among the significant scientific results from IUE data were the first large scale studies of stellar winds, accurate measurements of the way interstellar dust absorbs light, and measurements of the supernova SN1987A which showed that it defied stellar evolution theories as they then stood. When the mission ended, it was considered the most successful astronomical satellite ever.
The human eye can perceive light with wavelengths between roughly 350 (violet) and 700 (red) nanometres. Ultraviolet light has wavelengths between roughly 10 nm and 350 nm. UV light can be harmful to human beings, and is strongly absorbed by the ozone layer. This makes it impossible to observe UV emission from astronomical objects from the ground. Many types of object emit copious quantities of UV radiation, though: the hottest and most massive stars in the universe can have surface temperatures high enough that the vast majority of their light is emitted in the UV. Active Galactic Nuclei, accretion disks, and supernovae all emit UV radiation strongly, and many chemical elements have strong absorption lines in the UV, so that UV absorption by the interstellar medium provides a powerful tool for studying its composition.
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